Welcome to BYC! I used to put mine out by 8 weeks...as long as they are fully feathered. One thing I love about this age is that they sleep all flopped over on each other like puppies! So cute! Eventually they roost and don't do this.
First of all, how many chickens do you have? Were the feathers from the same chicken or multiple chickens? What type of environment do you live in? A neighborhood or rural? Are there trees and woods the chickens may have fled to? They may not all be dead or taken but hiding instead.